Process for accelerating metallurgical reactions

ABSTRACT

APPARATUS INCLUDING MEANS FOR ADJUSTING VERTICALLY THE LEVEL OF A MECHANICAL STIRRING MEMBER WITH RESPECT TO THE VERTICAL LEVEL OF A MELT, E.G. THE VERTICAL LEVEL OF THE INTERFACE BETWEEN THE TOP SURFACE OF AN IRON MELT SURFACE ESPECIALLY IN A CIRCULAR UPRIGHT LADLE WITH A DISCHARGE APER-   TURE, AND METHOD OF USING SUCH STIRRING MEMBER, E.G. TO ENHANCE OR ACCELERATE CONTACT AND REACTION BETWEEN SUCH MELT AND FLOATING INGREDIENTS, TO CARRY OUT METALLURGICAL REACTIONS, AS WELL AS TOUGH CAST IRON CONTAINING SPHERICAL GRAPHITE PRODUCIBLE THEREBY.

May 23, 1972 F. KRAEMER ET AL PROCESS FOR ACCELERATING METALLURGICAL REACTIONS Filed March 17, 1969 3 Sheets-Sheet 1 INVENTORS KLAUS DIETER HAVERKAMP FRIEDRICH KRAEMER JORN MANDEL JURGEN MOTZ SlEGFRlED MAYER KLAUS ROHRIG HANS-PETER SCHQLZ HILMAR WEIDENMULLER ATTORNEYS.

May 23, 1972 F. KRAEMER ET AL 3,664,8

PROCESS FOR ACCELERATING METALLURGICAL REACTIONS Filed March 17, 1969 5 Sheets-Sheet 2 INVENTORS KLAUS DlETER HAVERKAMP FRIEDRICH KRAEMER Q JORN MANDEL ::1* JURGEN MOTZ a SIEGFRIEDMAYER KLAUS ROHRIG HANS'PETER scHqLz HILMAR WEIDENMULLER ATTORNEYS.

F. KRAEMER ETAL May 23, 1972 PROCESS FOR ACCELERATING METALLURGICAL REACTIONS Filed March 17, 1969 5 Sheets-Sheet 5 INVENTORS TER HAVERKAMP KRAEMER KLAUS DIE FRIEDRICH JQRN MANDEL JURGEN MOTZ SIEGFRIEQ MAYER KLAUS ROHRI HANS-PETER s LZ BY HILMAR WEIDENMULLER 4 N ATRNEYS.

gm wwl United States Patent Oflice 3,664,826 Patented May 23, 1972 3,664,826 PROCESS FOR ACCELERATING METALLURGICAL REACTIONS Friedrich Kraemer, Mulheim, Jorn Mandel and Siegfried Mayer, Gelsenkirchen, Klaus Rohrig, Essen, Hans- Peter Schulz, Hattingen, Hilmar Weidenmuller and Klaus Dieter Haverkamp, Gelsenkirchen, and Jiirgen Motz, Ratingen, Germany, assignors to Rheinstahl Huttenwerke, Essen, Germany Filed Mar. 17, 1969, Ser. No. 843,868 Claims priority, application Germany, Mar. 23, 1968, P 17 58 038.0, P 17 58 039.1, P 17 58 040.4, P 17 58 041.5

Int. Cl. C21c 7/02 US. Cl. 75-50 14 Claims ABSTRACT OF THE DISCLOSURE Apparatus including means for adjusting vertically the level of a mechanical stirring member with respect to the vertical level of a melt, e.g. the vertical level of the interface between the top surface of an iron melt and slagging or the like ingredients floating on such iron melt surface especially in a circular upright ladle with a discharge aperture, and method of using such stirring member, e.g. to enhance or accelerate contact and reaction between such melt and floating ingredients, to carry out metallurgical reactions, as well as tough cast iron containing spherical graphite producible thereby.

The present invention relates to and has among its objects an appaartus for adjusting vertically the level of a mechanical stirring member with respect to the vertical level of a melt, and especially the level of the interface between the top surface of an iron melt and slagging or the like ingredients floating on such surface in an upright substantially cylindrical ladle having a discharge aperture, and methods of using such stirring member to carry out metallurgical reactions, as well cast iron producible thereby.

Numerous known metallurgical reactions of various kinds have in common the fact that the reaction components lack suflicient natural flow capability. Hence, frequently additional means are employed in an attempt to achieve rapid, intimate, and thorough mixing at least of the molten bath constituents and, as far as possible, an intermixing thereof with the other reaction materials which may be present.

A known type of such means or apparatus chiefly consists of a ladle or vessel which receives the metal bath or melt and which undergoes corresponding accelerations owing to translatory or rotational, partly also periodically direction-reversing, motion of such vessel, said accelerations causing the thorough mixing of the reactants involved owing to the inertia of such reactants as compared with the movement of the ladle. It is true that quite good results can be achieved with these types of apparatus, but the high costs of setting up and operating the equipment and the complicated manipulations necessary are considered decisive disadvantages.

No doubt, arrangements where the vessel containing the molten bath remains stationary and intermixing of the reactants is brought about by an agitating motion of the bath or melt are obviously more advantageous. Various embodiments of agitating devices are known for accelerated and/or improved carrying out of metallurgical reactions.

However, to the extent that electrodynamic forces are utilized for these agitating devices, the metallurgical vessel require a special shape. Also, no sufficient movement of the molten bath can be achieved where the device makes useof the injection of gases by means of known types of blowing lances. On the other hand, where injections of gases are carried out through porous hearth bottoms, the durability of the bricks of this type apparatus is insufiicient.

German Pat. 1,190,479 discloses a mechanical agitating and pumping arrangement for accelerating physical-chemical processes in molten baths, said arrangement consisting of a lower vertical suction pipe and at least one esseritially horizontal discharge pipe arranged laterally above and flow-communicating with the suction pipe. The arrangement rotates within the molten bath so that the melt is drawn from the lower portion of the ladle into the opening of the vertical suction pipe located in the lower portion of the ladle and is forced out again through the horizontal discharge pipes. Owing to this pumping action, a circulation flow of the molten bath takes place in the ladle. At the same time, there is a certain amount of agitating motion on account of the horizontal discharge pipes, but, as one can gather from the details stated, an obviously lesser significance is attached to said agitating motion.

Good results can be achieved with the arrangement of said German Patent as regards acceleration of metallurgical reactions. The treatment takes place in a ormal ladle so that additional re-ladling operations necessarily involving temperature losses are obviated. The light and portable device can be taken to the individual ladles. That is why it is very convenient in use and has a relatively low energy requirement.

The essential disadvantage of this German patent arrangement resides in the fact that the agitating and pumping elements are made of pipes, thus constituting a hollow body heavily washed by the melt on the inside and on the outside. The rather high operating temperatures of the device in conjunction with the abrupt temperature changes in treatment intervals severely shorten its life so that the costs of repair and renewal represent a considerable portion of the total operating cost.

A similar arrangement is shown in US. Patent 2,290,- 961, in which a tank car-mounted pivotable vacuum vessel in the form of a horizontal cylinder with pointed longitudinal ends is provided with air introduction nozzles fo'ragitating treatment of an iron melt or with a rotary mixing member in the form of an inverted T-beam or impeller for the same purpose. IIn the case of the impeller, either a solid horizontal beam or one containing pumping passages therein for pumping the melt, may be used, the beam being carried by a vertical shaft or supporting extension. To adjust the level of the beam, for example with respect to the level of the interface of the melt and slag floating thereon, this arrangement has the disadvantage that the beam must be physically replaced by another beam having the desired different length of vertical shaft or supporting extension. Especially where vacuum treatment of the melt is intended, the replacement of one beam by another of a different length of vertical shaft or supporting extension obviously will cause costly interruptions in terms of energy loss and time loss. Because of the very shape of the ladle and its normally sealed condition, eflicient mixing is limited and problems arise because of the confined space above the melt to accommodate the voluminous slag constit nents and volatile slag reaction products.

In Japanese Published Utility Patent No. Sho 40/26,- 248, published Sept. 7, 1965, a similar rotary impeller or inverted T-beam is shown for use with iron melts. Here, however, the impeller is extended into the melt well below the surface of such melt and not at any interface between the melt and slag which might float on top of the melt. No means for adjusting the vertical level of the impeller with respect to the body of the melt or of accommodating voluminous slag constituents are shown.

It has been found, in accordance with the present invention, that an agitating device may be provided, having a drive motor and a vertically adjustable vertical drive shaft on which a beam-shaped agitating element consisting of reinforced refractory material is arranged transversely or horizontally, for accelerated and/or improved carrying out of metallurgical reactions.

The mixing device according to the invention is especially effective for carrying out the most varied types of metallurgical reactions, particularly reactions taking place in metal melts in stationary ladles although also in other metallurgical vessels such as hearth furnaces or crucible furnaces. While the main mixing movement, corresponding to the height of the beam-shaped mixing member which rotates in the horizontal plane, is carried out only in a relatively narrow zone, based on the depth of the bath, a vigorous circulatory flow movement is nevertheless imparted to the entire bath which in a short time leads to complete homogenization of the metal melt. The mixing device is thus advantageously able to be used for example for the addition of alloying metals, for deoxidation, for carburization and similar procedures wherein it is of primary importance to obtain a uniform distribution in the metal melt.

The mixing device, however, also causes a significant horizontal flow so that the device is also very suitable for reactions between the metal melt and solid or liquid reactants which rest on the surface of the metal melt.

The mixing device is particularly suitable for reactions with slags which rest on the surface of the metal melt, during the removal of undesired secondary elements from the melt.

The mixing device may be modified and embodied in various specific forms. Generally, it is advantageous to envelop the lower part of the vertical driving shaft with a refractory material, such as where the lower part forms a structural unit with the horizontal beam-shaped mixing member, the unit being connected with the upper portion of the drive shaft in exchangeable or replaceable manner. The beam-shaped mixing member should preferably have a compact configuration which, in its longitudinal axial cross section, has a ratio of length to height between 2.521 and 1:1, e.g. 2.3 or 2.5:1, and in which appropriate cross sections at right angles to the longitudinal axis have a circular or rectangular form with rounded edges.

The usual refractory materials which may be selected on the basis of known principles depending upon the individual application are usable for the agitating element, thereby attaining high resistance to wear and appropriate resistance to temperature changes. It is preferable to provide for reinforcement of the refractory material of the agitating element in the form of a cooling line, e.g. for special cases involving very high bath temperatures and/or relatively long periods of treatment with short intervening rest periods.

The agitating device is, in particular, employed for treating molten baths contained in stationary ladles. For this purpose, it will be suitable to select the length of the beam-shaped agitating element so that it is between the 0.26-fold and 0.65-fold value, preferably between the 0.3'5-fold and 0.50-fold value, of the inside ladle diameter (at the level of the agitating element). In this case, the agitating device will be especially easy to operae when mounted on a cap piece covering the ladle, the drive shaft with agitating element of course extending through the cap piece and being vertically adjustable.

It may be suitable in special cases, for instance with very large steel ladles, to keep the length of the agitator beam or paddle as short as possible so that the aforesaid proportioning to the ladle diameter need not be observed.

In this case, the agitating device and especially the agitating beam or element is used to impart an additional translatory motion on a horizontal plane corresponding to the molten bath surface.

A further surprising advantage of the invention lies in the fact that the above-described agitating device enables, to a completely unexpected extent, acceleration and improvement in the elfectuating of such metallurgical reactions to be carried out, due to material exchange at the boundary layer or interface between the molten bath surface and the superimposed solid or liquid reactants, in particular slags or fine-grained buoyant compounds, floating on the melt surface. For optimum attainment of this end, a further feature of the invention is to lower the agitating device into the ladle only to the point at which the beam-shaped agitating element is immersed during the agitating operation to at least half its own height, but not more than just complete immersion into the molten bath. Considerable relative motions between the two phases are brought about by such agitation in the boundary zone or interface between the liquid molten bath and the adjoining reactant floating on the surface thereof.

Although the agitating element rotates practically in the surface zone only, the molten bath becomes homogeneous throughout. It has been found in accordance with the invention that the efficiency of the agitating element decreases with increasing depth of immersion. For this reason it is preferred that the depth of immersion of the beam-shaped agitating element should not be more than 1.5-fold its own height, measured from its bottom edge, during the agitating operation.

In the drawing,

FIG. 1 is a schematic side view, partially in section, of a ladle containing a metal melt having slagging ingredients or the like floating thereon, provided with a stirring member in the form of a horizontal beam-shaped element carried by a vertical shaft operatively mounted on a cover above the ladle for independent rotational as well as vertical displacement, in accordance with one embodiment of the invention;

FIG. 2 is a schematic side view similar to that of FIG. 1 of a modified arrangement in accordance with the invention provided with an adjustable slag baffle depending from the cover and a slag overflow aperture at the upper end of the ladle;

FIG. 3 is a schematic side view, partially in section, of a portion of an arrangement similar to that shown in FIG. 1, illustrating flow paths and flow directions of the melt and slag or the like ingredients in the ladle during rotation of the beam-shaped element located in the vicinity of the melt surface; and

FIG. 4 is a schematic top view, partially in section, of the embodiment of FIG. 3, showing the flow path trajectories and velocities of the melt and slag or the like ingredients during rotation of the beam-shaped element;

The following is a detailed description of the invention by way of a practical embodiment in connection with FIG. 1 of the drawing.

The agitating device has a drive motor 1 driving a vertical shaft 3, 4 via a gear unit 2. Transversely arranged on this shaft is a horizontal beam-shaped agitating element 5 composed of refractory material provided with internal reinforcement, e.g. in the form of a metal tube 131: (shown in phantom) which may also serve to conduct via shaft 3, 4 a cooling fluid therethrough for cooling the shaft and the element.

A preferred refractory material which may be cast to form the element may consist of 33 percent of SiO 60 percent of A1 0 3.5 percent of CaO, 1.5 percent of Fe' O and 1.3 percent of alkalies. This material is mixed with water until it is just flowable and cast into a form- Work in which the reinforcement, e.g. tube, is positioned. Then the cast is air-dried for approximately one day.

A chemically binding refractory material, option-ally preferred, consists of 26 percent of SiO 69 percent of 5 A1 0.9 percent of P 0 1.3 percent of Fe O 1.5 percent of TiO;, and 1.2 percent of alkalies. This material is tamped into a mold containing the reinforcement together with 5 to 6 percent of a chemical binding agent, e.g. monoaluminum phosphate [AlH '(-PO or phosphoric acid [H 'PO In certain cases, the agitating element can also be made of graphite.

The lower portion 3 of the drive shaft has a refractory coating and forms a constructional unit with the beamshaped agitating element 5, said constructional unit being interchangeably connected to the upper portion 4 of the drive shaft for replacement if and when necessary, The agitating element 5 may be so designed that the ratio of the length l to the height h is 2: 1, i.e. in terms of a section taken along the longitudinal axis; the cross sections at right angles to the longitudinal axis preferably have a circular form. The rotational speed of the drive shaft 3, 4

should be adjustable to provide, for example, speed rates of 49, 74, and 99 r.p.m.

If the duration of an individual melt treatment considerably exceeds about 45 minutes, or if the time interval between the individual treatments is less than about half an hour and if high bath temperatures are involved, it may be desirable to cool the reinforcement, e.g. tube 13a, with air. For this purpose, a pair of concentric tubes in the form of connecting piece 13 leading from a cooling air source (not shown) may be provided, which flow communicates as a double cooling line with tube 13a (shown in phantom) which in turn extends into the beam-shaped agitating element 5 through the drive shaft 3, 4, the cooling air flowing via one of said concentric tubes into and through the reinforcement, e.g. tube 13a, of the agitating element 5 and being exhausted via the other of said concentric tubes.

The agitating device is mounted on a cross plate 6 of a supporting structure in the form of vertical supports 7. The cross plate can be vertically adjusted via main adjustment means 7a, e.g. connecting bolts for attaching plate 6 to bolt seats or holes provided on supports 7. A reversible drive motor 8 provided with appropriate gearing acts on the upper portion 4 of the drive shaft for vertical fine adjustment of the beam-shaped agitating element 5 independently of the rotational movement of shaft 4.

In this regard, gear wheel 20 provided with appropriate disc guides 21 is mounted on vertical shaft 22 for rotation therewith yet is appropriately keyed, by means not shown, in slot 23 to permit vertical displacement of Wheel 20 axially along slot 23 independently of the rotation of shaft 22. Gear wheel 20 meshes operatively with gear wheel 19 fixed to the rotatable collar 17 having external threads along the lower portion thereof. Collar 17 is mounted in stationary nut 18 provided with internal threads matching the external threads on collar 17. The upper end of shaft 4 is operatively mounted on the pressure bearing 24 situated at the upper portion of collar 17. Thus, as wheel 20 drives wheel 19 in response to the rotational direction of reversible drive motor 8 transmitted via shaft 22, collar 17 will be rotated correspondingly within fixed nut 18. This will cause upward or downward axial movement of collar 17, as the case may be, with respect to nut 18 and in turn upward or downward axial movement of shaft 4, carried thereby via bearing 24, independently of the rotational movement of shaft 4. Furthermore, as wheel 19 is displaced axially with collar 17 so also will wheel 20 be displaced along shaft 22 due to the guiding relation between disc guides 21 and the ad jacent periphery of gear wheel 19.

In a manner similar to the axial displacement of wheel 20 along shaft 22, shaft 4 is displaceable vertically with respect to the gearing 2 of motor 1 due to the provision for the slot 16 in shaft 4 to which the gear wheel 14 is keyed via key 15. Therefore, as shaft 4 is raised or lowered axially along with collar 17, key will ride in slot 16 and permit rotational movement of gear wheel 6 14 to be transmitted to shaft 4 without interruption regardless of the axial position of shaft 4 and slot 16 with respect to the axially fixed gear wheel 14, i.e. within the longitudinal limits of slot 16.

Alternate means for effecting the raising and lowering of shaft 4 will occur to the artisan aware of the invention.

Hence, nut 18 can remain fixed from axial displacement by suitable guides yet be provided with an external gearing meshing with gear wheel 20 while a portion of collar 17 can be provided with a key riding in a stationary vertical slot mounted on the framework for motor 8. In this way, as nut 18 is rotated collar 17 will be displaced axially without being rotated.

On the otherhand, a rack and pinion connection can be similarly provided.

Such rack and pinion can even be provided to raise and lower the entire assembly on plate 6 in lieu of the bolts or the like 711.

Also, supports 7 can carry appropriate pulleys and cables, and contain vertical tracks in which plate 6 can ride while the pulleys are rotated to raise and lower plate 6 via the cables in the manner of a conventional elevator.

An additional feature is to provide vertical worm gears along supports 7, so as to coact with appropriate threaded apertures in plate 6 whereby to obtain vertical displacement of plate 6 by suitable rotation of such vertical worm gears.

All of these means for achieving vertical displacement are appropriately able to raise and lower either plate 6 or collar 17 and in turn shaft 4 in a more or less infinitely variable manner within the limits of displacement intended, whereby to obtain fine adjustment of the vertical level of shaft 4 and consequently of shaft 3 and element 5 with respect to the melt to be treated. On the other hand, the bolt means or the like, 7a, used for adjustment of plate 6 with respect to supports 7 can only achieve step-wise changes in the vertical level in question.

The step-wise adjustment means 7a, or the like, may be designated coarse or main adjustment means while the infinite adjustment means 17, 18, 19 or the like, may be designated fine adjustment means.

The supporting structure carrying the agitating device is mounted on the cap piece or ladle cover 9 such that the drive shaft portion having the agitating element 5 connected thereto extends through the cover 9, e.g. in an axially slidable yet independently rotatable manner. The cap piece 9 covers the ladle 10 and keeps temperature losses to a minimum. The cover 9 may be provided with a feed hopper 15a if desired. The ladle 10 contains the molten bath 11 and the reactant 12, for instance some slag, which float on the melt or bath surface. The agitating element 5 is arranged in the boundary zone or interface between the two phases by reason of appropriate axial displacement of shaft 4 and/or plate 6 and is immersed into the molten bath up to approximately of its own height h. The inside diameter of ladle 10 at about the level of the element 5 is designated D.

The above-described agitating device can be used for the most varied metallurgical reactions. Some examples are set forth hereinafter.

For the purpose of carburizing a cast-iron heat, coke breeze is fed to the ladle and the cap piece carrying the agitating device is placed on the ladle after the iron has been tapped. It is preferred in this connection to work with a low speed first, for instance at 49 revolutions per minute, to avoid too turbulent an evolution of gas and too heavy a generation of dust. The speed can be increased later on, as the artisan will appreciate.

Similarly, the usual alloying constituents can be quickly charged with good results, for instance pure nickel into liquid copper, silicon into liquid aluminum, ferro-silicon, ferro-manganese or ferro-chromium into molten iron, etc. Good results are obtained with precipitation deoxidations in molten iron baths, for instance by adding shot aluminum, ferro-silicon, and the like, since, on the one hand, a quick and uniform distribution of the melting bath is achieved and, on the other hand, the agitating device highly favors the rise of deoxidation products to the bath surface.

Especially good results are obtained with reactions between a molten iron bath and superimposed liquid slags.

Starting with a blast-furnace pig iron having 0.27 percent of manganese, 0.052 percent of phosphorus, 0.008 percent of sulfur, and 0.035 percent of titanium, it has been possible to produce a cast-iron premelting bath having a composition of less than 0.08 percent of manganese, less than 0.035 percent of phosphorus, less than 0.008 percent sulfur, less than 0.015 percent of titanium, and less than 0.008 percent vanadium. In this case, a total of 86.2 kg. of hematite fine ore and 24.8 kg. of sodium carbonate were added to each (metric) ton of pig iron. The procedure for adding was such that first 60 percent of the fine-ore quantity was batched with constant agitation, thereby converting the silicon and manganese into slag. After that, sodium carbonate and fine ore were alternately added in batches for the purpose of dephosphorization with agitation continuing so that the phosphorus also reached the aforesaid low value after completion of the slag reaction. This was followed by another addition of sodium carbonate for desulfurization. The desired final silicon content of the cast-iron premelting bath was determined by an addition of ferro-silicon. All aforesaid process cycles can be carried out continuously and consecutively within a period of approximately 60 minutes, the temperature losses amounting to approximately,l50 C. The finished cast-iron premelting bath is especially well suited for the production of nodular cast iron having a vastly ferritic structure already in as-cast condition even in the case of thin-walled castings.

For the purpose of desulfurizing open-hearth pigiron, pulverous calcium carbide was charged onto a pig-iron melting bath. The agitating element was immersed into the pig-iron melting bath up to approximately half its height.

(a) With an initial sulfur content of 0.1 percent, a final content of 0.009 percent is reached after an agitating period of approximately 6 to 8 minutes, corresponding to a desulfurization degree of approximately 90 percent. The amount of calcium carbide consumed was approximately 1 percent of the amount of pig iron. During the 4 treatment, the temperature of the pig iron only dropped from 1390 C. to 1380 C.

(b) With an initial sulfur content of the pig iron of 0.05 percent, a sulfur content of 0.009 percent is reached after an agitating period of approximately 6 to 8 minutes. corresponding to a desulfurization degree of 82 percent. The amount of calcium carbide consumed was 0.52 percent of the amount of pig iron.

In the embodiment shown in FIG. 2 which is basically the same as that of FIG. 1 the vertical adjustment means, cover and beam-shaped mixing element are present, but in addition thereto a slag overflow aperture 25 is provided in the upper edge of the wall of the ladle 10 as well as a vertically adjustable slag baflle or guide member 26 which is disposed operatively in cover 9 in the vicinity of aperture 25 to guide slag 12, or the like, outwardly through aperture 25 as may be necessary depending upon the particular reactions intended with respect to the melt or bath 11 and the desired control of quantities of slagging ingredients which develop during the mixing. The ratio of the length l to the height h in this embodiment may be 2.3:1.

Slag baflle or guide member 26 may be mounted on cover 9 to permit vertical displacement from an upper position out of contact with the slag 12 to the lower position shown in FIG. 2, for operative guiding of the adjacent portion of slag 12 toward the overflow aperture 25 whereupon under the flowing movement of the slag in consequence of the rotation of element 5 such slag will pass through aperture 25 and leave the ladle 10. Any

suitable means may be used to control the vertical displacement of the slag baflle 26 as the artisan will appreciate, such as a rack and pinion assembly or one of the other arrangements described above for vertical displacement of shaft 4 or plate 6.

The embodiment of FIG. 2 of the invention is particularly applicable for carrying out a process for the production of a pig iron having especially low percentages of manganese, phosphorus, sulfur, titanium and vanadium, and whose composition ranges from 3.5 to 4.6% carbon, 0 to 3% silicon, less than 0.10% manganese, less than 0.040% phosphorus, less than 0.010% sulfur, less than 0.015% titanium and less than 0.008% vanadium. Such a pig iron offers distinct advantages, especially in the production of cast iron containing spherical graphite and having a substantially ferritic structure.

In cast iron containing spherical graphite, a ferritic structure used to be obtained by the heat treatment of the finizhed castings. More recently the practice has been to produce spherical graphite cast iron, which has a ferritic structure in the cast state, and which thus does not require expensive heat treatment, by setting out from types of pig iron having low contents of manganese and other pearlitizing impuriites (Jurgen Motz and Kurt Orths in Giessereiforschung 1967, pp. 109-124). Additional requirements are a low phosphorus content to improve the notch impact toughness, a low sulfur content to lower the magnesium consumption and improve the notch impact toughness, and a low titanium content to prevent interference with the formation of spherical graphite. '7 In the production of pig iron for the above-mentioned purpose it is thus necessary for the contents of manganese, phosphorus, sulfur, titanium, vanadium and other accompanying elements to be kept as low as possible. Accordingly, pig iron grades are being offered which have a gradated maximum manganese content, e.g., less than 0.14% Mn, or less than 0.10% Mn, or less than 0.05% Mn. The phosphorus content and the sulfur content are also similarly gradated in these known types of pig iron.

Pig iron grades having the composition in question cannot be produced directly in the blast furnace, even when smelted from extremely pure and expensive ores.

In one known process, the blast furnace pig iron is placed in a converter and there purified with gaseous oxygen, using a blowing lance. In this process, silicon and manganese are first slagged, and then phosphorus and, inevitably, carbon too, are removed. Accordingly, the iron has to be recarburized by the addition of carbon.

In another known process, the Sorel process, highgrade iron ore is reduced in the electric furnace with anthracite coal. Pure titanium oxide is won from the slag and the pig iron is then deoxidized in the induction furnace, recarburized, and then desulfurized.

The known processes suffer from the main disadvantage that they involve a plurality of steps, and that dilferent treatment apparatus and working means are successively needed, which entail a correspondingly high cost of installation and operation.

This particular embodiment of the invention achieves the production of a pig iron having the above-stated composition starting from a blast-furnace iron, by using a beam-shaped mixing element and ladle arrangement of the foregoing type.

In this embodiment first fine ore is added to the molten iron tapped from the blast furnace into a static ladle, with stirring via the mixing element in the boundary zone between the bath and the' slag, until the desired manganese content is reached, then with continued stirring in the boundary zone, the pohsphorus is removed by the addition of soda and fine ore, and then, with continued stirring in the boundary zone, the bath is desulfurized by the addition of a known desulfurating agent, such as soda.

Advantageously, by mere stirring in a zone extending only partially into the slag area, and especially extending only slightly percentagewise (with reference to the bath depth) into the molten iron, an extremely effective exchange of material can be achieved between all of the iron and the slag, in all steps of the process. Although very large quantities of slag develop in the process, i.e. according to this embodiment of the invention, the speed of reaction is high and utilization of the slag is very good. The carbon content is not appreciably affected by the treatment, so that recarburization of the treated iron is not necessary.

The process of this embodiment can be improved in various ways. As a rule, a siliceous alloying agent, such as ferrosilicon, is added immediately after the desulfuration, preferably before any removal of slag, so as to adjust the required silicon content. Even without removing any of the oxidizing slag a surprisingly high silicon yield is achieved.

Even in the slagging of the manganese a considerable amount of slag develops, which is preferably drawn off automatically when a certain level in the ladle is reached, i.e. via the conjoint use of the slag aperture and baffle 26 of the apparatus of FIG. 2. This quantity can be controlled by the controlled addition of the fine ore so that the removal of the manganese will be accomplished with certainty down to the desired final content, whereupon the titanium and vanadium present will also have been removed or slagged as well. In like manner, it is preferable to control the amount of slag developing in the phosphorus slagging by the controlled addition of the fine ore and/ or soda, and to cause excess amounts rising above a certain level to run off automatically as noted above.

The instant process embodiment of the invention becomes especially simple if, even between the individual steps in the process (silicon and manganese slagging, phosphorus slagging, desulfuration, resiliconizing) there be no complete removal of the slag that is present. At the same time the ladle can be closed with the cover on which the necessary stirring apparatus and the feed aperture are provided, so that the temperature losses can be kept low. The entire process is then continuous, and can be performed with a correspondingly small consumption of time, yet with controlled removal of slag quantities by, reason of the slag baffle and ladle aperture used conjointly with the beam-shaped stirring element of the invention.

By use of the stirring apparatus contemplated herein, therefore, a rapid exchange of material between the phases involved is achieved as well as a homogeneous molten metal, with such apparatus being of the simplest possible construction and having a long service life.

, In the following Table 1 a comparison is made of four different heats from the blast furnace in connection with this embodiment of the invention.

In the case of a heat having the 48.3 metric tons weight, the procedure in detail was as follows using an arrangement analogous to that of FIG. 2. First about 2.5 metric tons of hematitic iron ore having an Fe content (total) of about 67% was added gradually, portion by portion, to the heat tapped from the blast furnace into a static ladle, while the heat was being stirred. This addition amounts to about of the total amount of iron ore added. The ore was added in the form of a fine ore having a grain size of at most about 10 mm. Shortly after the beginning of the addition of ore, a voluminous slag formed, which automatically ran off through an aperture in the ladle when it rose above a certain level in the ladle. This slag first removes the silicon, and other highly oxygen-refining attendant elements, particularly titanium and vanadium, from the iron. As the addition of ore continues, at a rate determined by the amount of slag forming, the slag also carries off the manganese, so that by the end of this stage of the process the heat has attained a manganese content below 0.08%. During this treatment the heat has been constantly stirred in the boundary zone between the bath and the slag by the beam-like stirring element rotating while immersed to about /2 to of its thickness into the metal. The length of the stirring element amounted in this case to 800 mrn., at a ladle diameter of 2200 mm. At the beginning of the treatment the stirrer was driven at 30 rpm. After the liquefaction of the iron ore the speed was raised to 70 rpm.

Then, while stirring continued in the boundary zone, soda and fine ore were added portion by portion, alternately, for the purpose of dephosphorization. The amount of soda was of the total shown in the table, subdivided into three individual additions of about 6.2 kg./ ton of raw iron each, alternated with additions of ore of about two times 8.6 kg./ton of raw iron each (2X 10% of the total quantity). The last addition of soda was followed by the addition of 17 kg. of ore/ton of raw iron (about 20% of the total amount). After each addition there was a period of waiting until the fluid slag resulting from the exchange of material had formed, when then ran off in part.

While the stirring in the boundary zone continued, another batch of soda weighing 6.2 kg./ton of raw iron was put in for desulfuration, and then, at increased rotary speed rpm.) of the stirring element, and without any special removal of slag, an appropriate quantity of ferrosilicon (75% Si) was added to adjust the desired silicon content. The silicon yield amounted to 92%. With a treatment time of about 60 minutes, the temperature losses amounted to only C.

The embodiment of FIGS. 3 and 4 of the invention is best illustrated in terms of a process for the desulfura- TABLE 1 Amount of tine Amount ore of soda (kg/t. (kg/t. In starting molt, (percent) Amount of of raw of raw raw iron (13.) iron) iron) Mn P S Ti V Average analysis after treatment; 0. 08 0. 035 0. O08 0. 015 0. 008

Table 1 gives the total amount of ore and soda added 70 tion and deoxidation of carbon-containing iron heats in during the stirring treatment, as well as the starting contents of manganese, phosphorus, sulfur, titanium and vanadium. From the bottom line it can be seen that the final contents are below the required maximum values for these elements.

a ladle, in which a circulatory flow is produced in the hot metal, which is directed downwardly at the wall of the ladle and upwardly at the center of the ladle.

Mechanically driven ladle units of the type noted heretofore have in recent years acquired what is no doubt chief importance in the desulfuration of iron. The ladles are set in motion in such a manner that the accelerations which occur, and which vary to some extent in degree and direction, cause the metal and the desulfurating agent to blend together due to the mass inertia of the bath and of the desulfurating agent. -If the degree of utilzation of the desulfurating agent is good, such driven ladles permit the achievement of final sulfur contents of 0.01% or less, setting out from initial sulfur contents between 0.08% and 0.12%, depending on the method of melting in the acid cupola furnace. Important disadvantages, of course, are the high cost of the erection of the equip ment, the complicated handling in connection with a particular location, and considerable power requirements.

In other known processes, the expense is lower because the ladle and its contents are stationary and a circulatory flow is induced in the bath by introducing a gas through a blowing lance or through porous bricks disposed in the bottom of the ladle as discussed above, occasionally with the desulfurating agent being also blown in with the gas. Aside from the fact, however, that the gas introduced produces an undesirable cooling action, either the bath movement that could be induced proved to be inadequate or the service life was too short.

Although the mechanical stirring and pumping apparatus of the above-mentioned German Patent 1,190,479 is able to induce a circulatory flow of the hot metal in the ladle, such that desulfuration can be performed in a regular teeming ladle, the pumping device has the disadvantage of short service life discussed previously.

The arrangement shown in said US. Patent 2,290,961, because of the peculiar tank orientation and non-uniform shape in horizontal cross-section, is unfitted for efficient flow of the melt and slag and is unable to attain convenient manipulation of the ingredients, controlled removal of slag during the operation, etc.

All the prior-art processes and apparatus have tried to achieve an intensive blending of the desulfurating agent wth the hot metal, evidently based upon the theory that the stronger the agitation, the better will be the desulfuration.

In connection with the particular embodiment of the invention in question, it has been found that desulfurating and deoxidizing of carbon-containing iron heats can be carried out extremely effectively in a static ladle or other such vessel for ferrometallurgical purposes, i.e. of the type contemplated for instance, in FIGS. l-4. The treatment can thus be performed either in the melting unit itself, e.g., in the crucible of an induction furnace or in the forehearth of a cupola furnace, or preferably in the teeming ladle. The invention provides not only an inducing of a circulatory flow in the molten iron, but also the producing of an appropriate flow in the desulfurating agent, without producing a turbulent blending of the desulfurating agent with the hot metal. It has been found in fact that intensive blending of the desulfurating agent with the hot metal is by no means necessary for the achievement of a high degree of desulfuration. Instead, it is quite suificient for both of the reactants to remain separate from one another and for each to undergo a separate pronounced circulatory movement, so that the reaction is restricted to a boundary surface or interface, but it is nevertheless very intense.

Thus, the desulfuration-and deoxidation of carbon-coutaining iron heats may be carried out in a static ladle or other such vessel for metallurgical purposes, in which a circulatory flow of the hot metal is provided which is directed downwardly at the ladle wall and upwardly at the center of the ladle. The instant process differs from the prior art in that a charge of a finely granular material containing calcium and carbon is placed on the surface of the bath, and in that a stirring movement takes place in the boundary zone and is so chosen that the hot metal at the surface has a flow which propels the particles of 12 finely granular material on the bottom of the charge toward the edge of the ladle and there causes the accumulation of a heap of particles along the very slope of which the particles slowly move back to the stirring center individually or in the form of coarser aggregations.

The finely granular material used can be, for example, calcium carbide or other known finely granular desulfurating agent such as lime nitrogen (technical CaCN containing some CaO, regarded in Germany as Kalkstickstotf) or mixtures of fine limestone and coke breeze.

This embodiment of the process of the invention is preferably performed so that the stirring in the boundary zone produces such a flow of the individual units of volume of the iron at the bath surface that the trajectory of the units of volume of the iron, which is sharply curved in the area of the stirrer, has a constantly diminishing curvature which causes a centrifugal thrust at the ladle margin, and furthermore so that the trajectory of the units of volume of the top charge is similar as regards the change of curvature. At the same time the velocity of the units of volume of the iron and the velocity of the units of volume of the top charge are preferably maintained in a value ratio that is greater than 2:1 and is preferably greater than 5:1.

The stirring movement should be produced insofar as possible so that the top charge of finely granular material forms a continuous blanket so as to avoid loss of heat by radiation and prevent oxidation of the metal.

In order to achieve the desired flow in the iron bath and in the desulfurating agent, the beam-shaped stirring element is best adjusted to such a height that, during the stirring, it is immersed into the metal at least to the extent of half of its own thickness, but is not more than barely completely immersed therein. In this manner, although the desulfurating agent is moved in the stirring center, it nevertheless forms advantageously a continuous blanket on the surface of the hot metal. In order to obtain an optimum desulfurating and deoxidation it is preferable to proportion the length of the beam-like stirrer t the diameter of the ladle. In this regard, it is best for the length of the stirrer to amount to between 0.25 and 0.65, and preferably to between 0.35 and 0.50, times the ladle diameter, as noted previously. The rotary speed of the stirrer or beamshaped element is preferably adjustable so that the extremities of the stirrer will assume peripheral velocities ranging from 1.8 to 3.5 m./sec., and preferably between 2.0 and 2.8 m./sec.

With specific reference to the embodiment of FIGS. 3 and 4, the beam-shaped element or stirrer 5 is 460 mm. long, 350 mm. thick and 250 mm. wide, so that the ratio of its length l to its thickness or height h is 1.3:1. The beam-shaped stirrer is immersed to a depth of 340 mm. into the molten iron and extends 10 mm. into the top charge of for instance powdered calcium carbide. The length l of the beam-shaped stirrer 5 is equal to 0.42 times the ladle diameter D. The ladle 10 has a vertical axis and a corresponding continuous upright confining wall of substantially constant radius of curvature at any given axial level and the stirrer 5 is centered for rotation substantially about the vertical axis of the ladle. The rotary speed of the drive shaft 3 of the stirrer is adjustable to preferred values in such a manner that the extremities of the stirrer 5 can assume peripheral velocities ranging from 1.8 to 3.5 m./ sec., and preferably from 2.0 to 2.8 m./sec., as aforesaid.

When the described stirring device is composed of reinforced fire clay, approximately 60 desulfuration treatments lasting from 8 to 12 minutes were regularly performed at iron bath temperatures between 1380 and 1420 C.

According to this embodiment of the invention, a top charge 12 of a finely granulated material containing calcium and carbon, e.g., calcium carbide, is placed on the surface of the molten metal 11, and a stirring movement is executed. in the boundary zone. This movement is so adjusted that the molten iron at the surface of the bath has such a flow that it propels the calcium carbide particles towards the margin of the ladle 10 and there builds up a pile 27 of particles along the slope 28 of which the calcium carbide particles move back individually or as coarser aggregations towards the stirring center. The calcium carbide top charge 12 forms advantageously a con- .subjected to a ferritizing heat treatment, usually in two stages, but this entails an increase in the risk of reject due to distortion, scaling and the like, in addition to the heat treatment costs.

In former times, efiorts were made to produce pig iron tinuous blanket over the hot metal, thereby minimizing types of select composition from which a cast iron contemperature losses, which amount to about to 30 C. taining spherical graphite could be produced, which in the under the conditions stated above, on the basis of expericast state exhibits a substantially ferritic structure, even ments actually performed. in thin-walled castings. Such types of pig iron must be FIG. 3 also indicates diagrammatically the conditions of as free as possible from accompanying elements other flow in the hot metal and in the calcium carbide top 10 than the carbon and silicon they contain, since such elecharge. According to the wide arrows 29, the flow of iron ments interfere with the formation of spherical graphite or is directed downwardly at the ladle walls and upwardly have a perlite-stabilizing eifect, even in low concentration, in the middle of the ladle. On the other hand, as a result or they diminish toughness due to solution embrittlement of the pileup 27 of particles and slope 28, a circulatory of the ferrite. flow takes place as indicated by the thin arrows 30, which 15 Low-manganese types of pig iron having graded maxiis an important requirement for the obtaining of the outmum manganese contents, graded maximum phosphorus standing results actually achieved in the desulfuration, contents and graded maximum sulfur contents are availwhich will be clear from a consideration of Table 2. A able commercially, which are characterized also by very blending together of the two reactants does not take place low concentrates of other accompanying elements. Manthroughout; the reaction takes place instead entirely in a ufacturers of cast iron containing spherical graphite can boundary layer or interface therebetween. thus select the types of iron that meet their particular FIG. 4 illustrates, by flow arrows in the top view requirements. shown, the trajectory 31 of a unit of volume of iron and Furthermore, it is known quantitatively (see the aforethe tnajectory 32 of a unit of volume of the top charge, as mentioned Jiirgen Motz and Kurt Orths in Giessereiforwell as the corresponding rotational and centrifugal veschung 1967, pp. 109-24) what weight per percentage locity vectors 33, 34 and 35, 36, respectively. As to the unit of certain impurities adversely afiects the toughness trajectory 31 (iron), the curvature which is strong in the of cast iron in the cast state. Important in this regard are area of the stirrer 5 diminishes constantly towards the not only the above-mentioned manganese and phosphorus, margin of the ladle 10, so that a centrifugal force compobu Particularly the contents of pp lead, antimony. tin nent is created, and the slowed propulsion of the calcium and arseniccarbide particles produces a pileup in the area of the mar- Although yp of B g iron that f 10W in e P Y- gin of the ladle. Trajectory 32 (calcium carbide) is simg elements are avaliable as startlhg material, and ilar in its basic form (flow pattern). FIG. 4 is intended though. as Stated, the relationships e to a great extent to show, of course, only on a fundamental basis, the naunderstood, hitherto the y types of lhdustrlally 111211111- ture and magnitude of the motional actions in question. 35 fectul'ed typ of cast iron that have been known are From FIGS. 3 and 4 can be appreciated the considerthose which Produce ill castings having a Wall thickness able relative velocities of the two reactants which prevail 0f 5 in the east state (sand molds) a Peefhte 6011- i h b u d l Thi fa tor, together i h h tent that is definitely above 20%, and usually runs even circulatory flow in the iron and in the top charge, tends 40 around to optimize the exchange of material as desired. This is Cast Iron cohtalhlhg p e graphite particularly true because the ladle is more or less of unitough in the cast state, as provided in accordance with form diameter throughout its height while being of subthis Particular embodiment of the Present Invention, 1s stantially round or circular configuration in horizontal distinguished from the Prior art in that the following e011" cross-section, in relation to the centrally disposed beamtents of the specified impurities are Present! lead under shaped ti rin l t, 45 0.002%, titanium under 0.04%, chromium under 0.01%, Some of the results of desulfuration treatments perarsenic under 0.002%, Copper under 0.01%, tin under formed on cast-iron heats are compiled in the following 0.002%, vanadium under 0.01%, and antimony under Table 2: 0.002%, and in that the cast iron in castings made in sand TABLE 2 Stir- Initial Final ring Quantity Periph- Depth Loss in sulfur sulfur time of iron Percent Rotary eral oi immer- Starting temperacontent, content, (min- (in metric of C802 speed velocity sion temperature percent percent utes) tons) added (r.p.m.) (m./sec.) (mm) l/D 1 ture 0.) C.) 0. use-0.112 0. 003-0. 004 10 6.1 1.2 74 1.78 340 0.41 1, 410-1,420 25-30 0100-0113 0. 003-0. 005 4 8.0 1.0 72 1. 74 340 0. 41 1, saw-1,390 15-20 0100-0120 0 007-0. 009 2 8.0 1.2 86 2.07 350 0.41 1,40,04,410 10-15 0. 082 0. 00a 10 20.7 0. 97 70 2. 35 320 0. 39 1, 420-1, 425 15-20 0.086 0.045 12 9.5 1.2 0. 84 330 0.25 1,400-1,420 25-35 1 (Ratio of length of stirrer to ladle diameter.) A further embodiment of the invention relates to a molds and having a Wall thickness of '5 mm. has a pearlite cast iron containing spherical graphite, which is tough in content in the cast state of less than 10%. the cast state, and which contains from 3.0 to 4.2% car- I accordance with th instant embodiment of the t0 silicon, less than 01% manganese, less invention, it has been surprisingly found that the producthen 004% P P less than (101% Sulfur and tion of a cast iron containing spherical graphite, whose to 007% i h l castings are to have a virtually entirely ferritic structure apphcanmis a cast .comalmpg 5 and hence a high toughness in the cast state, even in the graphic is deslred winch fsuffiplenfly h1g1? uctlhty case of slight wall thicknesses, is not assured by the mere to assure good forming qualities 1n the castings. It 1s fact that the concentration of the impurities interfering known that a perfect formlng of spherical graphite and h a1 hi f d f a substantially ferritic structure is necessary for this pur- W 1th SP enc grap te oimatloli 9 the lmpuntle's pose. A ferritic Structure is increasingly more difli lt to hitherto regarded as pearlite stabilizers 1s kept low. EVlachieve as the wall thickness of the castings decreases. dently still othe hithefto llilieeoghiled, influences are Consequently, the finished castings have previously been at ork,

Using an apparatus of the type shown in FIG. 2, the manufacture of a cast iron according to the instant embodiment of the invention, is set forth below by way of example:

A blast-furnace pig iron (about 50 tons) containing 4.4% C, 1.35% Si, 0.17% Mn, 0.067% P, 0.022% S, 0.037% Ti, 0.015% V, 0.0015% Pb, 0.008% Cr, 0.001% As, 0.008%Cu, 0.001% Sn, and 0.001% Sb, is tapped (1350-1450 C.) into a ladle, and at first fine ore is added with stirring in the boundary zone between the pig iron (at about 1300-1350 C.) and the slag until the desired manganese content is achieved. Then, with continued agitation in the boundary zone, soda and fine ore are added to flux out the phosphorus. While stirring in the boundary zone between the pig iron and the slag continues, the molten pig iron is desulfurized by the addition of a known desulfurizing agent, such as soda. The treatments to this point take a total of only about 60-85 minutes and the temperature drop is only about .100-150" C. Thereafter, ferrosilicon is added to adjust the silicon content to the desired higher level, requiring only an additional -10 minutes.

In detail the procedure is such that, to a pig-iron quantity of 48.3 metric tons (1340 C.), a total of 86.2 kg. of fine ore (grain size equal to or less than mm.) and 24.8 'kg. of soda per ton of pig iron are added.

To remove the manganese, approximately 60% of the total quantity of fine ore is added portion by portion, and the slag thus produced is allowed to run off through an overflow trough (see FIG. 2) to the extent that it rises above the top level.

To remove phosphorus, about 75% of the total amount of soda is added in portions alternating with the balance of the fine ore. Here, again, some of the slag is to be allowed to overflow from the ladle.

To remove sulfur, about 25% of the total amount of soda is added.

The treatments to this point actually take only about 70 minutes and the temperature drop is only about 125 C.

Immediately thereafter ferrosilicon (75 Si) is added, with stirring, in order to adjust a silicon content of 1.3%. This step only takes an additional 8 minutes but no further temperature drop Occurs since the solution heat of ferrosilicon counteracts radiation and conduction heat losses.

For the stirring in the boundary zone between the pig iron and the slag, the stirrer or beam-shaped element is adjusted in height so that the same extends partially into the pig iron bath and to a slighter extent into the fluid slag.

As a result, a preliminary cast iron is obtained containing the following elements: 4.3% C, 1.26% Si, 0.07% Mn, 0.038% P, 0.007% 5, 0.013% Ti, 0.008 V, 0.0015% Pb, 0.008% Cr, 0.001% As, 0.008% Cu, 0.001% Sn, and 0.001% Sb.

From this preliminary cast iron, a starting iron for cast iron containing spherical graphite was prepared by remelting in a medium-frequency induction furnace with the addition of ferrosilicon. This starting iron was treated with an iron-magnesium-silicon alloy (about 30% Mg) by dipping process, and it was then inoculated with 0.8% ferrosilicon 75 Si).

The chemical composition of the iron before casting was the following: 3.86% carbon, 2.48% silicon, 0.08% manganese, 0.034% phosphorus, 0.006% sulfur and 0.051% magnesium. The rest of the elements were contained in the same percentages as they were in the preliminary cast iron. With the iron at a temperature between between 1390 and 1360 C., plates having a Wall thickness of 5, 12 and 30 mm. were cast in an oil sand mold. The pearlite content in the 5 mm. plate amounted to 35%, while the 12 and 30 mm. plates contained only traces of pearlite. The rest of the ground mass consisted of ferrite. The pearlite content of these three plates was Notch impact toughness (at 20 C., specimen from 30 mm. plate)-2-2.5 Kp./m./cm.

Transition temperature38 to 43 C.

0.2% elastic limit 6 =25 to 30 Kp./mm.

Tensile strength 'GB--=4O to 45 Kp./mm.

Elongation at rupture 6 -=20-25% Brinell Hardness BH Kp./mm.

(A) Generally, in connection with all of the embodiments of the invention, the starting blast furnace iron may contain in percent by weight:

Carbon 4.40-4.86 Silicon 1.5 Manganese 03 0 Phosphorus 0.l Sulfur 0.030 Titanium 0.060 Vanadium 0.025

Remainder substantially iron.

and where the usual other impurities are also present, such iron may further contain:

Lead 0.001 Chromium 0.010 Arsenic 0.001 Copper 0.01 Tin 0.002 Antimony 0.002

(B) A conventional range of ingredients in a starting blast furnace iron, in connection with all of the embodiments of the invention, may include in percent by weight:

Carbon 4.40-4.86 Silicon 0.86-1.50 Manganese 0.08-0.12 Phosphorus 0.0410.056 Sulfur 0.0l20.030 Titanium 0.025-0.038 Vanadium 0.010-0.012

Remainder substantially iron.

and optionally the immediately above amounts of said other impurities (see A above), such that the final pig iron, before addition of ferrosilicon to adjust the silicon content, for example in the case of the embodiments discussed above in connection with FIG. 2 may contain in percent by weight:

Carbon 3.95-4.35 Silicon 0.01-0.07

Manganese 0.04-0.06 Phosphorus 0024-0035 Sulfur 0006-0010 Titanium 0.004-0.008

Vanadium 0.0030.005

Remainder substantially iron.

and optionally the same amounts of said other impurities as in the starting blast furnace iron (see A above), possibly with the chromium content being reduced to 0.008%.

In this regard, the amount of fine ore (e.g. hematite) added as contemplated for the various treatment steps: (the starting Si content in percent minus the final Si con- 17 tent in percent) times 100 kg. per ton of melt weight. Generally, the final Si content (before the alloying addition of ferrosilicon) is adjusted to less than 0.10%. The

amount of soda added is between about 25-30 kg. per 7.

furnace iron will preferably have less than 1.5% silicon content since higher silicon contents require higher amounts of fine ore to refine the silicon content down to the mentioned 0.10% silicon content and this entails temperature control difficulties. Of course, by reducing the silicon content to below 0.10% the titanium and vanadium contents are also reduced, and thus the manganese slagging is readily carried out.

Especially important in accordance with the invention is the use of the [foregoing starting blast furnace iron (see A above) to produce the aforementioned cast iron containing nodular or spherical graphite with a vastly ferritic structure, tough in the cast state and having less than 10% pearlite.

The advantages of uniform, thorough and efiicient boundary layer or interface mixing of the melt and slag within very short treatment times and With simple removal of slagging ingredients are achieved in accordance with the invention because of the flow paths and trajectories of the two phases (see FIGS. 3 and 4) made possible by the use of the beam-shaped mixing element in coaction with a ladle of substantially uniform diameter throughout its axial height and having walls of substantially circular configuration in horizontal section, such that the mixing element is positioned substantially coincidentally with the main vertical axis of the ladle (see FIG. 1). With the provision for a vertically adjustable baffie and ladle aperture (FIG. 2), the slagging materials can be run off conveniently and with a minimum of manipulation, i.e. merely by lowering the adjustable bafile into the slag phase to guide the slag, under the flow path conditions generated by the mixing element, out through the ladle aperture.

In particular, the vertically adjustable mixing element permits much more accurate as well as continuous adjustment of the mixing element position with respect to the intenface between the two phases (FIGS. 1 and 2) while the adjustable baflie and the ladle aperture (FIG. 2) usable in conjunction therewith attain full control and simple manipulation of the slag level under the existing operating conditions and flow paths (FIG. 3 and 4), all without interruption of the overall multiple step slagging operation. The prior art devices are devoid of these structural conjoint features and thus inherently cannot attain these advantages, nor does the prior art suggest the make-up of the cast iron containing spherical graphite which is tough in the cast state and essentially completely ferritic in nature, with less than 10% pearlite.

It will be appreciated that the instant specification, drawings and examples are set forth by way of illustration and not limitation, and that various modifications and changes may be made without departing from the spirit and scope of the present invention.

What is claimed is:

1. In the method of accelerating as well as enhancing metallurgical reactions by mechanical stirring of a melt, the improvement which comprises rapidly and intimately mixing the constituents of a melt disposed in an upright vessel having a vertical axis and a corresponding continuous upright confining wall of substantially constant radius of curvature at any given axial level by conduct ing continuously the portion of the melt in the vicinity of the melt surface in rotational flow to cause such melt to be centrifugally outwardly urged, in an arcuate trajectory to the confining wall of said vessel, thence downwardly along such wall to the bottom of said vessel and inwardly to the center portion of the vessel and in turn upwardly along such center portion back to the vicinity of said melt surface substantially solelyunder the urging influence of a relatively elongated mixing member in the form of a solid beam-shaped mass of refractory material rotating about said vertical axis which is substantially perpendicular to the longer dimension of such mixing member while such mixing member is situated in the vicinity of the surface of said melt and inserted at least partially thereinto so as to extend substantially transversely thereof.

2. Improvement according to claim 1 wherein said mixing member is inserted into said melt to such an extent that the lower edge of said mixing member is spaced from the surface of said melt by a vertical distance of at most 1.5 times the axial width of said mixing member.

3. Improvement according to claim 2 wherein said mixing member is inserted into the melt to the extent of 0.5 to 1.0 times the axial width of said mixing member.

4. Improvement according to claim 1 wherein granular ingredients to be admixed with said melt are situated on the surface of said melt and under the conditions of rotational fiow the lowermost portions of such ingredients in the vicinity of the melt surface form an interface therewith and are caused to be centrifugally outwardly urged in an arcuate trajectory to the confining wall of said vessel during which time intermixing exchange between said melt and said ingredients takes place at said interface, With the portions of such ingredients which reach said confining wall of said vessel being upwardly urged to form a substantially annular radially inwardly and downwardly sloping mass and in turn flowing along the upper portion of said mass inwardly and downwardly to the center portion of the vessel and back to the vicinity of said melt surface.

5. Improvement according to claim 4 wherein said arcuate trajectory of said melt and said arcuate trajectory of said ingredients both have a constantly diminishing curvature in the direction toward said confining wall of said vessel.

6. Improvement according to claim 4 wherein said ingredients form a continuous blanket on the surface of said melt.

7. Improvement according to claim 4 wherein the ratio of the flow velocity of said melt to said ingredients is at least 2: 1.

8; Improvement according to claim 4 wherein said mixing member is rotated at a peripheral velocity of between about 1.8 to 3.5 meters per second.

9. Improvement according to claim 4 wherein said melt constitutes an iron melt and said ingredients constitute calcium and carbon.

10. Improvement according to claim 9 wherein said ingredients constitute calcium carbide.

11. Improvement according to claim 4 wherein said melt constitutes an iron melt and said ingredients constitute hematite fine ore and sodium carbonate.

12. Improvement according to claim 4 wherein said melt constitutes an iron melt and wherein fine hematite ore constitutes said granular ingredients so as to achieve manganese slagging, then soda and additional hematite ore are added as further granular ingredients to achieve phosphorus slagging, and thereafter soda is added as still further granular ingredient to achieve desulfurization.

13. Improvement according to claim 12 wherein said iron melt initially constitutes a blast furnace iron melt containing by weight:

4.4-4.86% carbon less than 1.5% silicon less than 0.30% manganese less than 0.1% phosphorus 19 less than 0.030% sulfur less than 0.060% titanium less than 0.025% vanadium remainder substantially iron.

14. The improvement according to claim 1 wherein the metallurgical reactions are effected using an upright vessel having a cylindrical wall and provided with a vertically displaceable beam-shaped elongated mixing member rotatable about a vertical axis, of a length about 0.25 to 1 0.65 times the diameter of said vessel and thickness about 0.4-1 times its length.

20 References Cited UNITED STATES PATENTS 2,290,961 7/1942 Heuer 75-55 X 3,278,295 10/1966 Ostberg 75-61 2,397,737 4/1946 Heuer 75-55 L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner U.S. Cl. X.R. 

